DE4126443C2 - Turbine impeller layered welds - Google Patents

Description

The invention relates to turbine and generator parts used in steam power plants be used, and in the special process for repair and manufacture of low-alloy steel disks and runners to increase their lives duration.

Steam turbines and generators' rotors are usually low alloyed steels and have a number of outwardly protruding Fir tree structures or fir trees (steeples) on the perimeter of the Runners are designed for fastening blades. During the These fir trees can be operated by steam-generated corrosion agents corrode and erode or through dirt or steam in the turbine wear out. Such destructive mechanisms sometimes occur by pitting and breaking the fir trees and the surrounding panes area or noticeable by significant metal wear. You can lead to the destruction of the entire turbine runner, resulting in great costs for the user arise.

Recent developments in welding, such as B. the use of improved alloys and welding techniques with low thermal energy consumption, made it possible to restore turbine runners from low alloy material so that new fir trees can be incorporated into the welds. The following writings are given as a reference:
Clark et al., "Experiences with Weld Repair of Low Pressure Steam Turbine Ro tors" 47th American Power Conference, Chicago, Illinois, printed by Westing house Electric Corporation, Power Generation, Orlando, Florida. and Clark, et al., "Development of the Technologies for High Pressure Rotor Weld Repair," Westinghouse and Mitsubishi Tech. Seminar, Takasago, Japan, July 1987.

Notwithstanding such techniques with which an expensive removal of the Impeller can be reduced, bring fir tree structures through low-alloy welds were reconstructed, little or no Improvement in corrosion behavior or service life if they are exposed to the same environmental conditions that pitting or that Breakage in the original impeller.

Impeller repairs by craftsmen are also known, in which the zer disturbed area of the impeller cut out and a new impeller part inserted is welded. This is described in U.S. Patent 4,633,554. Such techniques are also not suitable, the corrosion behavior, or the wear of the repaired impeller and may require further expensive repairs do.

There were also hard coatings from STELLITE on turbine wheels with egg plasma transfer arc welding technology (plasma transferred arc welding technology). This is in "New Services for Industrial Turbi nes, No. 31, (Winter 1989) ". By melting a powder in the plasma masystem can create a strong metallic connection on a turbine impeller can be achieved which has sufficient erosion resistance against solid particles in the Hot gas shows. While this technique is a bit cheaper in terms of mind corrosion, targeted attacks by corrosion occur in places on where the top layer has broken off. Corrosion in such areas is generally worse than the corrosion on the surface of the impeller, if no top coat was applied at all.

The object of the invention is to provide a longer-functional impeller that Resists pitting and breaking in the turbine environment and longer can be produced inexpensively.  

The task is accomplished with the help of an impeller solved according to claim 1.

The invention is implemented on the impeller of a rotor of a steam turbine, the a ring part made of low-alloy steel that contains less than 6 weight per percent of alloy additives including chromium, molybdenum and vanadium holds. The invention is implemented by layered welding layers, which be attached to the ring part, the layers increasing Contained by weight of stainless steel, and also by a fir Tree area made of an alloy containing chrome, which is on the layers is attached and has a thickness of more than 1.25 cm to prevent corrosion between to reduce the ring part and the fir tree area.

In this context, it should be pointed out that JP 62-113804 (A) is known, the outer periphery of a turbine wheel with a variety of one to coat individual layers of pure metals, each with a differently strong ero have tendency to sion. It is also known from DE 32 12 185 C3, on the äu Outer circumference of a turbine impeller layered weld layers with decreasing Apply Cr portion.  

Further features and advantages of the invention result from the following the description of preferred embodiments in connection with the Claims and the drawing. Show it:

Figure 1 is a section through an embodiment of an impeller according to the invention, which shows a low-alloy ring part together with a welded fir tree area, which is attached via a layered layer of welds.

Figure 2 is a section through an impeller of another embodiment with a ring element made of layered layers of welds and with egg nem tree area, which is made by a separate weld.

Fig. 3 sections of three differently manufactured embodiments of impellers in side view with parts consisting of fir trees;

Fig. 4 is a partial section of another embodiment of a Laufra, which shows how the layered weld on the impeller to protect the wheel from wear and corrosion can be expanded.

The invention extends the life of steam turbines and Generator components, specifically for impeller parts made from low alloy steel exist as the base metal, with less than 6 weight percent alloy additions including Cr, Mo and V are provided. According to the invention a layered steel layer is attached to a ring element of the impeller brings, which consists of a plurality of different welding layers, in the one an increased proportion by weight of Cr is introduced with each layer. On the steel layers a fir tree area is formed, which is made of a Cr alloy Optimization of the life-extending properties of fir tree exists.

In another preferred embodiment of the invention, a Impeller of a steam turbine with a ring element that consists of a Steel with low alloy additions of less than 6 percent by weight including Cr, Mo and V. The impeller has been layered on the ring element-attached welds, which increase the weight stainless steel part included. A fir tree is marked on this layer brings, which consists of a chrome-containing fir tree alloy. The Layering of this version has a thickness greater than approximately 1.25 cm is causing the corrosion between the ring element and the fir tree area is minimized due to the different alloy proportions.

The invention also teaches a method of preparing the rotor one Steam turbine to optimize the life of the fir tree area where at a ring element is made available for steel-containing reason material with less than 6% by weight alloy additives including Cr, Mo and V exist. The process includes a step in which one steel layering is attached to the ring element. The stratification in this method has a number of welds on the layer contains a higher proportion by weight of Cr. A fir tree area that Containing Cr-containing fir tree material is then on the layering attached, after which the construction is complete.

In Fig. 1, a cross section is shown of the rotor portion by a large rotor of a steam turbine of low-alloy steel, of less than 6 percent by weight of alloying elements has. Typical alloys used in low pressure steam turbine rotors are listed in Table 1 below. In addition, alloy steels with Cr-Mo-V are generally used in the high pressure area of steam turbines and can be treated similarly to the method used in this invention.

Table I

Low alloy wheels

In the preferred method, a ring element is preferably a disk with a reduced diameter made of a base material 10 . In order to build up a layered weld 12 with a different steel content, the welding is started with a filler metal of the impeller material in accordance with Table I. After a run, a weight fraction of Cr of more than 1 percent, in particular even of more than 3% Cr, containing layer material, preferably in austenitic stainless steel, is preferably used for the welding. After a second pass, a second small portion of layer material containing chromium or stainless steel is added to the fill material. After each further run, the proportion of layer material containing chromium or steel is increased until the filler material preferably consists of 100% layer material made of chromium or stainless steel. Preferably, the layered material of the layered weld contains at least two percent by weight Cr to improve wear resistance and at least 12% Cr to improve the corrosion resistance of a fir tree structure 20 . Austenitic stainless steels useful for the invention are listed in Table II. However, other corrosion-resistant stainless steels can also be used for this purpose.

With the help of the invention, repairs can also be carried out by welding be performed. The same applies to the manufacture of both types of equipment, namely High temperature and low temperature alloy rotor or for generator run fer. Mixtures of stainless low-alloy steels can be welded by adding two wires of filler material in a continuously changing proportion len are mixed in by changing the relative feed rate so that each welding pass is only slightly different from the previous one Pass is. In a preferred modification of this technique, for quasi-continuous operation, a selection of filler wires is used, whereby each time after a fixed number of runs on other filling material wires is switched. Viewed from the stratification, the sizes should be differences in the composition should be as small as possible, since then the Ge Overall effect improved by minimizing electrochemical cells.

Suitable welding techniques for this invention are narrow gap welding, Protective metal gas welding, submerged arc welding and tungsten inert gas welding. The preferred technique is Tungsten Inert Gas Welding because it does Control of the interpass temperature allowed and the production relative defect-free welds. The following parameters are used Tungsten inert gas welding to apply the layering and / or tan nenbaum areas of the invention used.  

Table III - Tungsten inert gas basic parameters

electricity 150-180 A. tension 20-25 V Gas flow 425 l / min (15 CFM) Wire diameter for filling material 2.4 mm (3/32 inch) Shielding gas Argon 99.8% Tungsten electrode 2% thorium

In this connection, the following writings are given: T. B. Jefferson and G. Woods, "Metals and how to weld them", James F. Lincoln Arc Welding Foundation, 2nd Edition (1983); and Metals Handbook, Volume 6, "Welding, brazing and soldering", 9th edition ASM (1983).

In a preferred embodiment according to FIG. 1, the tan tree area, ie the area of the impeller disk which contains one or more tan tree structures, consists of a welded structure made of stainless steel, which thus extends as a layered weld 12 into the finally produced fir tree 20 , as shown with the fir tree structure 24 in FIG. 3. In this structure 24 , the fir tree alloy 14 has similar or better mechanical properties than the base material 10 . Here, a simple welding process is achieved in that circular profiles are welded ge. If the base material 10 has better mechanical properties than the fir tree alloy 14 , a fir tree structure 26 will be the better choice. In this embodiment, the base material 10 extends into the fir tree structure and the layered weld 12 is thinner. However, it is more difficult to maintain suitable corrosion resistance over longer distances. If the metallic properties of the alloy for the fir tree are generally poorer than those of the base material 10 , it may also be appropriate to make the layered weld 12 thinner, as shown in the fir tree structure 28 . In this exemplary embodiment, the layered weld 12 is generally adapted to the shape of the final dimensions of the fir tree 20 produced .

In another embodiment of the invention corresponding to FIG. 2, a fir tree alloy 14 made of stainless steel is connected in a block with a layer device 12 . In each of the above embodiments, the layered weld 12 can be formed so that a good initial configuration is achieved before the fir tree alloy 14 is applied.

To achieve reasonable corrosion resistance, the thickness of the layered weld should be on the order of 1.25 cm or more, but preferably greater than about 2.5 cm, around the low-alloy washer 10 from the fir tree structure 14, preferably made of steel separate. If the thickness of the layer 12 is too small, a drop of water would act here as a corrosion cell and cover a large range of compositions, thus creating a very favorable situation for corrosion.

According to FIG. 4, a layered approach can also be used to protect the impeller disk against corrosion in critical areas. Each welding layer contains a different concentration of chromium in the layer alloy or in the stainless steel and can increase the distance between the stainless fir tree alloy 14 and the low-alloy base material 10 by the layered construction. The layers 18 should be long enough so that the distance from the exposed base alloy 22 to the stainless steel fir tree alloy 14 is greater than the longest water route. The thickness of the cover layers is not critical, but full coverage of the low-alloy ring element, as described in connection with FIG. 3, is preferred. In such an example, a stainless steel finish layer may be applied, which should be thicker than the lower layers, to allow minor surface damage without penetrating the lower, more easily corroded layers.

Alternatively, the lower part of the ring element made of low-alloy material be covered with one or possibly several layers consisting of  stainless steel of high concentration to form a protective layer. Such a configuration would be easy to manufacture, but would more sensitive to corrosion if the protective layer is made of rustproof Steel is injured.

The invention enables repair work to be carried out more easily, and also that the manufacturing process for the original equipment so is improved that fir tree structures optimal wear properties obtained when operating steam turbines and generator rotors. The description NEN welding techniques create a stratification in the composition between a preferably made of stainless steel fir tree area and a low-alloy impeller part, which locally reduces corrosion.

Claims (5)

1. Turbine impeller, consisting of a ring part ( 10 ) and a fir tree area with grooves and webs ( 20 ) made of a Cr alloy for receiving blades with fir tree feet, the ring part made of low-alloy steel, which consists of less than 6% by weight. % of alloy additives, including chromium, molybdenum and vanadium, with a welded-on part made of fir tree grooves and webs ( 20 ) with several layered weld layers ( 12 ) on the ring part ( 10 ), the percentage by weight of stainless steel with a Cr content being different Weld layer to weld layer from the ring part ( 10 ) up to the fir tree area increases with a total thickness of more than 12.5 mm. 2. Turbine impeller according to claim 1, characterized in that

• 1. that the base material contains nickel.

3. Turbine impeller according to one of the preceding claims, characterized in

• 1. that the majority of the layered welding layers is applied by gas welding by tungsten protection.

4. Turbine impeller according to one of the preceding claims, characterized in

• 1. that the difference in stainless steel in successive welding courses is more than 1% by weight, in particular at least 3% by weight.

5. Turbine impeller according to one of the preceding claims, characterized in

• 1. that in the area of each fir tree area ( 14 ) to the ring part ( 10 ) graded structure of the layered weld layers ( 12 ) is present.